Many existing engines include an intake port injection system for injecting fuel, e.g. liquid or gaseous, into the intake port for delivery to one or more engine cylinders. These engines may also include two intake valve ports and two exhaust valve ports for each cylinder. Consequently, each set of two intake ports are served by an intake inlet dedicated to the respective cylinder. In the dedicated intake inlet arrangement, the fuel is injected into the ports using one of three arrangements. First, a single dual stream injector may be used for each cylinder to direct a fuel spray at each port, such as disclosed in U.S. Pat. No. 4,982,716. The dual injector injects the fuel when the intake valve is closed. Second, a single injector without dual streams may be used but results in poor distribution. Third, one injector may be used for each port. Although achieving effective distribution of fuel, two injectors per cylinder is unnecessarily expensive and often difficult to position within the packaging constraints of the engine.
A shared or siamese port arrangement in combination with a single intake port design may also be used to limit the number of injectors by mounting one injector in the common intake inlet to the ports as disclosed in U.S. Pat. No. 5,477,830 issued to Beck et al. In this shared port arrangement, the intake port from adjacent cylinders share a common intake inlet. The fuel stream is injected into the intake air while the intake valve associated with only one of the cylinders is open and the other intake valve closed. As a result, the fuel charge is entrained by the high velocity air charge flowing into the cylinder associated with the open intake valve. However, Beck et al. only suggests an intake port injection system for an engine having only one intake port per cylinder.
Consequently, there is a need for an intake port injection system for a multi-cylinder engine having dual intake ports which minimizes the number of injectors while ensuring accurate and reliable fuel delivery to the cylinders.